Zika Disease - Archived EDEN Topic Page

Zika Disease - Archived EDEN Topic Page

This page contains information that was preserved in August 2017 when the EDEN website moved to this new system. The information here has not been, and will not be, updated. For more information on this topic, please use the EDEN Website Search function in the header. If you reached this page from a bookmark, please update that bookmark.

Zika disease in humans is caused by infection with the Zika virus which is transmitted most often by the bite of an infected mosquito. The mosquito species most likely to be involved in transmission in the United States and its territories are two “container mosquitoes,Aedes agypti (the yellow fever mosquito)and Aedes albopictus (the Asian tiger mosquito).

The disease was detected in Brazil, where it was linked to birth defects in the babies of women infected with the virus. The virus traveled to the states in infected travelers, and concern rose for the possibility of the vector-human-vector cycle to become established.

EDEN's response to the Zika threat

EDEN conducted an initial survey of delegates in February, 2016, to determine their interests, needs, and on-going Zika activities. The results suggested that a handful of states had begun both research and Extension education of both staff and the public, and that there were some specific needs from the Extension community. Among those needs were research on impacts of the virus on companion animals and information on how the Zika threat generally would impact summer Extension outdoor programs.

EDEN added "Zika" to the Hazard Type tag in the Resource Catalog, and cataloged the resources provided through the initial survey. EDEN also began developing the capacity to provide educational information to support member programs. With the direct assistance and involvement of Dr. Nick Place, EDEN ECOP Liaison and Extension Director for Florida Extension, Dr. Roxanne Connelly was asked to lead the initial effort, and to select a team of experts. Dr. Connelly and her team (listed below) have provided the information contained in the two background information pages first published on May 6, 2016: Zika Disease and Zika Virus and Vectors.

A webinar and additional forms of communication and support for Extension Zika programming are contemplated.

EDEN's Zika Resource Collection

The CDC Draft Interim Zika Response Plan was introduced by the Centers for Disease Control as they hosted a national teleconference with state health officials, state epidemiologists, state maternal and child health leads, and key local health department officials.for the continental United States and Hawaii on Friday, June 10, 2016. Updates will be provided as new ideas come to light or circumstances change. While all cases reported to date in the continental United States and Hawaii are travel-related, it is important to increase awareness and prepare now to respond to local transmission of Zika.

CDC Zika Interim Guidance for District and School Administrators

The U.S. Centers for Disease Control and Prevention (CDC) has developed interim guidance for kindergarten through Grade 12 district and school administrators for public health actions pertaining to the Zika virus infection. This guidance provides an overview of the potential roles and responsibilities of public health authorities and school officials, describes prevention measures that schools can take to reduce mosquito exposure, and provides information on response planning.

Transmission and Symptoms

Most people who are infected with the virus do not get sick. For those who do become ill, the symptoms that have been reported include fever, rash, joint pain, and conjunctivitis.Death from Zika infection is extremely rare. Complications can arise for pregnant women who are infected with Zika virus. The US CDC provides details and recommendations for pregnant women. http://www.cdc.gov/media/releases/2016/s0413-zika-microcephaly.html

The primary mode of transmission of Zika is from the bite of infected Aedes mosquitoes. There is evidence of transmission of Zika virus through sexual contact, from mother to child, and blood transfusions (http://www.cdc.gov/zika/transmission/).

"Imported" Cases of Zika

Imported cases of Zika are defined as those that occur when a person has travelled to an area where the virus is cycling among mosquitoes and the human population and contracted the disease there. Upon returning home, the person may become ill and visit a physician. If testing shows that they do have an infection with Zika virus, the case would be considered “imported” because they contracted the pathogen abroad, but are diagnosed in the US. For example, if you travel to Brazil and were bitten by an infected mosquito in Brazil, but were diagnosed with Zika virus in the US, then you would be considered an imported case.

"Local" cases of Zika

Local transmission of Zika virus means that the virus is circulating in mosquitoes found within the US, and that humans are infected when bitten by mosquitoes in their community. For example, if an infected mosquito bit you in your backyard and you were diagnosed with Zika virus, then you would be considered a local case. As of this writing (April 2016), the only cases of Zika that have been reported in the continental United States have been imported cases http://www.cdc.gov/zika/geo/united-states.html

Local transmission of the virus is occurring in the following territories of the United States: American Samoa, Puerto Rico, Marshall Islands, and the US Virgin Islands (St. Croix, St. Thomas, and St. John). For up-to-date information on areas with local transmission, visit: http://www.cdc.gov/zika/geo/index.html

Risk for the United States

Cases of Zika that are imported into the United States have the potential to contribute to local transmission. There is a period of about 14 days after being infected when mosquitoes can pick up the virus from humans. If someone with an infection is exposed to local Aedes mosquito vectors, the virus could then be picked up and transmitted by the local mosquito population. Areas with the highest risk of this occurring are those where populations of Aedes aegypti and Aedes albopictus occur. Many states are currently conducting mosquito surveys and updates on the distribution maps are expected.

On July 29, 2016, Florida Rick Scott reported 4 cases of locally acquired Zika in Miami-Dade and Broward Counties. Blood donation centers in Miami-Dade and Broward counties have stoped accepting blood from donors in the affected area until methods to screen blood or techniques to deactivate the virus in blood are put in place. Surveillance of human cases and mosquito texting is on-going and new information will be posted as it is released.

Reducing Risk

Travel

To reduce the risk of infection with Zika virus, travelers should consult the Centers for Disease Control (CDC) website for information on where active, local transmission is on-going http://wwwnc.cdc.gov/travel/page/zika-information. If travel is planned to an area where local transmission has been reported, then CDC guidelines should be followed regarding the use of insect repellents, bed nets, and protective clothing. The recommendations are included at the link shown above.

Effective and Ineffective Methods

Example of products that do not provide protection from mosquito bites. James Newman, University of Florida, Florida Medical Entomology Laboratory. Used with permission. Click for larger image.

There are many items on the market that make claims to repel mosquitoes or to eliminate mosquitoes from an area. Some items that will not offer protection from mosquito bites, or eliminate populations of mosquitoes includes mosquito repellent bracelets, necklaces and other jewelry; mosquito patches; bug zappers; consumption of vitamins; ultrasonic frequency-emitting devices; and homemade mosquito traps. The best protection from mosquito bites is to wear effective mosquito repellents. For details on selecting appropriate repellents, consult this EPA website: https://www.epa.gov/insect-repellents/find-insect-repellent-right-you.

Read also about controlling virus exposure by controlling the mosquito vector on this EDEN Zika Virus and Vectors page.

Zika disease in humans is caused by infection with the Zika virus which is transmitted most often by the bite of an infected mosquito.

Vector Mosquitoes

Photo credits: Aedes aegypti. James Newman, University of Florida, FMEL. Aedes albopictus. Sean McCann, University of Florida. Used with permission.

The mosquito species most likely to be involved in transmission in the United States and its territories are two “container mosquitoes", Aedes aegypti (the yellow fever mosquito) and Aedes albopictus (the Asian tiger mosquito). The two species can be distinguished by white markings on the scutum (thorax). A. aegypti has white markings in the shape of a lyre; A. albopictus has a prominent white stripe running the length of the scutum.

An estimated distribution of the occurrence of these two mosquitoes in the United States was provided by the US Centers for Disease Control (CDC). See Vector Distribution map below.

Container mosquitoes are also responsible for the transmission of chikungunya and dengue viruses to humans and dog heartworm to dogs and cats. Another mosquito, Aedes triseriatus, occurs in the same type of habitat and is responsible for transmitting La Crosse virus to humans. It is important for public health that everyone remain vigilant about removing items that might be attractive for the container mosquitoes.

Cycling between mosquitoes and humans

The virus cycles between mosquitoes and humans, and non-human reservoirs are currently unknown.

At this time, most of the local mosquito populations in the continental United States are not known to be transmitting the virus. Many states are collecting and testing mosquitoes for presence of the Zika virus. While there have been no positive mosquitoes detected yet, there is evidence that local transmission of the virus has occurred in south Florida, in Miami-Dade and Broward Counties. Four cases of Zika were reported from people with no travel history. A majority of the infections reported in the U.S. to date have been in people who have travelled to areas where the local mosquitoes are transmitting the virus, and then returned home after being infected.

"Container Mosquitoes"

Mosquito eggs can be seen above the water line in this container. Credit: Roxanne Connelly, University of Florida, FMEL. Used here with permission.

Container mosquitoes, such as Aedes aegypti and Aedes albopictus deposit their eggs on the sides of water-holding containers, just above the water line. Individual eggs are about the size of a grain of pepper and can be difficult to see. The eggs undergo a drying out period, and can remain dormant until the container becomes flooded. Eggs will hatch into larvae when the water level in the container rises and comes into contact with the eggs. Immature mosquitoes will live in water until they emerge as adults. Mosquito larvae (Photo) feed on organic materials including leaves, algae, and other nutrients that occur in the container. The larvae molt, or shed their skin, four times, increasing in size during each period between molts. The fourth time they molt, they undergo transformation to a pupa (Photo), which is very active in the water, but does not feed. Immature mosquitoes are also known as “wigglers” and “tumblers” because of the swimming movements they make in the water. After several days in the pupal stage, the adult mosquito emerges and begins a terrestrial life.

Photo credits: Mosquito larvae, Roxanne Connelly, University of Florida, FMEL. Mosquito pupa, Michelle Cutwa, University of FL, FMEL. Used here with permission of University of Florida

Adult Mosquito Behavior

Examples of “natural” containers include tree holes, bromeliad plants, and bamboo. Roxanne Connelly, University of Florida, FMEL. Used with permission of UF. Click for larger image.

Male and female adult mosquitoes feed on sugar sources (such as flower nectar) for energy. The females also feed on blood to provide nutrients to their developing eggs. Adult container mosquitoes don’t fly much over 500 feet from their aquatic habitat. Anyone being bitten while on their own property should check for water-holding containers as the mosquitoes are likely being generated very close to home. Generally, the female mosquito lays her eggs about 3 days after taking a blood meal, at which time, she seeks more blood to nourish the next batch of eggs. Each egg batch could include as many as 150 eggs. She can continue the blood-feeding and egg laying for as long as she survives. The females live about a month. Container mosquitoes are known to distribute their eggs amongst several containers. Often times containers will have eggs from more than one female.

More on mosquito containers

Some examples of containers where Aedes albopictus and Aedes aegypti can be found. Credit: Creative Commons. Click for larger image.

Containers are classified as almost anything that can hold water. Examples of common container types where these mosquitoes have been detected include tires, potted plant saucers, tree holes, bottles, cups, pet dishes, flower vases, bird baths, tarps, cisterns, trash cans, buckets, corrugated extension spouts, and clogged or bent roof gutters. Container types can be further defined as “natural” or “human made”. Natural containers include tree holes and bromeliad plants that collect water in their tanks. Human-made containers can include anything that is not naturally occurring that might be found in the yard or community. Some examples of container mosquito habitat are shown here.

Vector Distribution

Click for full sized image. This is a public domain image from the CDC website, acquired April 2016.

An estimated distribution of the occurrence of these two mosquitoes in the United States was provided by the US Centers for Disease Control (CDC). For US residents who live in the states where container mosquitoes are found, it is wise to begin mosquito source reduction efforts locally and within the community now even though local transmission of Zika virus has not been reported.

Vector Source Reduction

Container mosquitoes are responsible for transmission of many pathogens that cause disease, and source reduction should be a regular task around the home. Source reduction means removing the source of the mosquitoes, which in this case means water-holding containers. For items that can be discarded, conduct yard and neighborhood cleanup routines weekly. Make sure that any items that can be removed (bottles, cans, any trash that holds water) are appropriately discarded.

For small water-holding items that need to remain in place (bird baths, plant saucers, buckets, watering cans), clean them out weekly from April – November. These can be cleaned by (1) dumping the water and replacing it with clean water and (2) scrubbing the inside wall of the container to remove any mosquito eggs that may be attached.

For larger bodies of water such as cisterns, water collecting drums, rain barrels, and planters that do not have drainage holes, insect screening as a cover will prevent mosquitoes from depositing eggs inside the container, or a larvicide with active ingredients Bacillus thuriengensis israelensis(Bti) or methoprene can be used. The larvicide products come in the form of granules, briquettes, and donuts and will last a few weeks in the water holding receptacle. Make sure to follow label recommendations for application rates and sites. Products with these active ingredients can be purchased at local hardware and do-it-yourself stores. For abandoned pools and ornamental ponds, mosquito fish can be added which will consume the immature stages of the mosquitoes.

FMEL-Florida Medical Entomology Laboratory

Note: The Use Permission for the information and images made available on this page extend to all EDEN member Extension programs.

Photo credits: Aedes aegypti. James Newman, University of Florida, FMEL. Aedes albopictus. Sean McCann, University of Florida. Used with permission.

Published or Revised:11/20/2017

Author(s): Pat Skinner

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